Conventional precast concrete stairways exhibit a number of disadvantages. Very often, such stairs are constructed in a form or mold that has a step-shaped bottom surface for defining the steps and an open upper end into which the concrete is poured. This form creates a stairway that exhibits a heavy flat slab along its bottom surface. Such a stairway requires unnecessarily large amounts of concrete and is quite heavy. Moreover, because the bottom of the mold forms the steps, it is impossible to add a hardening or wear resistant material to the steps as they are forming in their wet condition. Such stair systems are also quite inflexible. The dimensions of each step form typically cannot be adjusted to match desired floor and building heights. A completely new form is required for each variation in height.
A stair system utilizing individually precast steps is known. In that system, steps are formed and then permanently cast into a pair of supporting side walls. Accordingly, worn or defective steps cannot be conveniently removed and replaced. Moreover, these steps are formed in an enclosed mold, which, again does not permit the addition of hardening or wear resistent materials to the concrete being cast. Additionally, this system does not permit the adjustment of tread depth and lateral width as well as riser height and width.
Certain of the above difficulties are successfully addressed by the precast stair system disclosed in my U.S. Pat. No. 4,995,205. Although that system exhibits significant improvements over the prior art, it typically employs a stringer structure that features step-shaped recesses for accommodating the steps. Such stringers must be carefully cast to closely conform to the shape of the steps. Imprecise casting can result in a defective structure. A simpler stringer structure and a quicker, more effective technique for releasably securing the steps to the stringer means are desired.